Biomedical Engineering Reference
In-Depth Information
Fig. 5
Biomechanical model, mandible and jaw-closing muscles
muscles (Fig. 5 ). These three pairs of muscles were taken into account to build
a mathematical model of the TMJ forces in order to increase the precision of the
results [ 39 ].
The masseter muscle, which is short and wide, presents two parts. The thick
surface masseter (noted sm ) arises from the anterior part of the zygomatic arch. Its
fibers are inserted into the mandible angle and constitute a powerful elevator. Its
direction contributes to mandible propulsion. The deep masseter (noted dm ), which
is smaller, arises from the posterior part of the zygomatic arch. Its fibers are inserted
into the lateral surface of the mandible coronoid process and remain almost normal
to the occlusion plane.
The medial pterygoid muscle (noted mp ) remains parallel to the inner side of the
mandible. It is inserted just above the medial surface of the lateral pterygoid plate
and into the lower and back part of the medial surface of the mandible ramus. It is a
powerful elevator that also helps in propelling and side to side movement of the jaw.
The temporal muscle arises from the temporal fossa, passes through the zygo-
matic arch and is inserted onto the mandible coronoid process. Broad and flat, it
can be subdivided into three bundles to model its action by three forces (Fig. 5 ).
The anterior bundle (noted ta ) simultaneously propels and lifts the mandible. The
medial bundle (noted mt ) whose fibers are virtually orthogonal to the occlusion
plane primarily lifts the jawbone. Finally, the fibers of the posterior bundle (noted
pt ), which also present some insertions on the TMJ meniscus contribute to the retro-
propelling movement.
2.2.2
Location of the Insertion Points, Directions of the Muscle Forces
Four dissections were carried out to investigate the contacts between the mandibular
condyles and the temporal bone, and the insertions of the six jaw-closing muscles
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